Here's one I'm thinking of suggesting once Cousteau vs. Irwin comes out: Dog the Bounty Hunter vs. Dick Tracy! A cop battle seems overdue, and those two are the most iconic I can think of (besides Robocop, but he's been done now...) Although both of these characters are known to operate on their own terms that fall outside of the main police's jurisdiction...

the founder and first ruler of the Kingdom of Hawaii vs the first sultan of Egypt/Syria, and the founder of the Ayyubid dynasty

I would love to see Kamehameha in a battle. love it when they go for historical figures on the more obscure end of things, like Zulu...
I would put Kamehameha against another island monarch, just so there's more connection. maybe King Minos of Crete (even though he's just mythological)
or Sukarno, the first president of Indonesia

Not sure if I've posted this before but an idea I had was John Kramer (Jigsaw) Vs Tomas de Torquemada (Leader of the Spanish Inquisition) I've seen a few people suggest Jigsaw should be in an ERB and this would be more interesting personally than anyone else I've seen people suggest he go up against.